The ethylene/(meth)acrylic acid copolymer resin and the ethylene/(meth)acrylic acid/(meth)acrylic acid ester copolymer resin, contain polar groups in the molecular chains thereof and adhere excellently to a metal such as aluminum or to any other resins having polar groups, such as nylon and polyester. The above resins further have excellent heat-sealing property and hot-tacking property in addition to toughness and flexibility. Therefore, the above resins have heretofore been used chiefly as sealant resins or adhesive resins such as laminate films or sheets, i.e., have been much used as stretch films for wrapping, like materials for packing candies and sweets, foamed polystyrene trays, and as materials for the paper containers for juices, liquors, etc., for the containers for bathing agents, for the containers for poultices and for the laminated tubes for toothpastes.
The formed articles such as the above laminated films can be, usually, produced by the line-forming such as extrusion coating/extrusion lamination by using an extruder.
Therefore, the high-speed workability (DD property, NI, etc.) of the starting resins greatly affects the productivity of the products, i.e., the cost of the products. However, the high-speed workability of the resins of these kinds is considerably poorer than that of the general-purpose low-density polyethylenes, and it has been strongly urged improve the workability.
In order to improve the high-speed workability, JP-T-2004-510871 proposes a resin composition obtained by selecting an ethylene/(meth)acrylic acid copolymer or an ethylene/(meth)acrylic acid/(meth)acrylic acid ester copolymer having a relatively small acid unit content, and blending about 5 to 45% by weight thereof with about 95 to 55% by weight of a low-density polyethylene.
The above resin composition surely improves the high-speed workability to some extent and, therefore, helps increase the productivity correspondingly but cannot strongly adhere to certain kind of polar base materials such as nylon base materials and, often, fails to reach a practicable limit strength. Therefore, limitation is imposed on its use.
In addition to the above problem, further, when a resin containing polar groups such as acid groups like the above copolymer resin is melt-extruded for extended periods of time, the resin adheres and stays in the resin flow passage of the extruder, and is partly gelled, deteriorated or decomposed producing stripes in the products, or causing gels or lumps to be mixed into the products resulting in the production of defective products. Further, when the operation of the melt-extruder is started again after the operation thereof has once been stopped, gelled and decomposed products of the resin in the resin flow passage are discharged over extended periods of time. Therefore, a tremendous period of time and products are wasted until normal products are obtained after the restart of the apparatus.
In the field of modern plastic molding, it is a trend to produce an ever increased kinds of products in ever decreased amounts, changing colors of the resins to be molded or changing the kinds of the resins more frequently then ever before.
In this case, for example, when the color or the resin is to be changed by using a blow-molding machine, a tainted contaminant due to the preceding resin remains in the seam portion that is joined when a hollow cylinder is formed in a parison fitted in the extruder. The contaminant due to the preceding resin cannot be easily removed, and deteriorates the appearance and physical properties of the molded articles.
In order to solve the above problems, a method has heretofore been employed according to which the interior of the resin flow passage in the molding machine such as the extruder is substituted with a purging agent which is obtained by blending a resin such as a high-density polyethylene, a low-density polyethylene, a straight-chain low-density polyethylene, a polystyrene or a polypropylene, or a mixture of resins thereof with a surfactant or an inorganic filler.
For example, Japanese Patent No. 3568327 discloses a purging composition obtained by blending a hydrophobic thermoplastic resin such as a polyolefin resin, a hydrophilic thermoplastic resin such as an ethylene/vinyl alcohol copolymer, and a crystal water-containing compound such as a hydrated calcium chloride in amounts of particular ratios.
Further, JP-A-3-207734 discloses a washing composition obtained by blending a polyolefin resin and a polymethyl methacrylate resin with one or two of a neutral salt of an organic sulfonic acid, basic magnesium carbonate, aluminum hydroxide or zinc carbonate in amounts of a predetermined ratio.